using System.Data.Common;
using System.Text.Json;
using Microsoft.Data.SqlClient;
using Microsoft.Extensions.Logging;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.ExternalSystems;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
using ZB.MOM.WW.ScadaBridge.Commons.Types;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
using ZB.MOM.WW.ScadaBridge.StoreAndForward;

namespace ZB.MOM.WW.ScadaBridge.ExternalSystemGateway;

/// <summary>
/// WP-9: Database access from scripts.
/// Database.Connection("name") — returns ADO.NET SqlConnection (connection pooling).
/// Database.CachedWrite("name", "sql", params) — submits to S&amp;F engine.
/// </summary>
public class DatabaseGateway : IDatabaseGateway
{
    private readonly IExternalSystemRepository _repository;
    private readonly StoreAndForwardService? _storeAndForward;
    private readonly ILogger<DatabaseGateway> _logger;

    /// <summary>
    /// Initializes a new instance of <see cref="DatabaseGateway"/>.
    /// </summary>
    /// <param name="repository">Repository for resolving database connection definitions.</param>
    /// <param name="logger">Logger for diagnostics.</param>
    /// <param name="storeAndForward">Optional store-and-forward service for cached writes; null disables buffering.</param>
    public DatabaseGateway(
        IExternalSystemRepository repository,
        ILogger<DatabaseGateway> logger,
        StoreAndForwardService? storeAndForward = null)
    {
        _repository = repository;
        _logger = logger;
        _storeAndForward = storeAndForward;
    }

    /// <inheritdoc />
    public async Task<DbConnection> GetConnectionAsync(
        string connectionName,
        CancellationToken cancellationToken = default)
    {
        var definition = await ResolveConnectionAsync(connectionName, cancellationToken);
        if (definition == null)
        {
            throw new InvalidOperationException($"Database connection '{connectionName}' not found");
        }

        var connection = CreateConnection(definition.ConnectionString);
        try
        {
            await connection.OpenAsync(cancellationToken);
        }
        catch
        {
            // OpenAsync failed (unreachable server, bad credentials, cancellation) —
            // dispose the just-created connection before the exception propagates so
            // it is not leaked (ExternalSystemGateway-010).
            await connection.DisposeAsync();
            throw;
        }
        return connection;
    }

    /// <summary>
    /// Creates the underlying ADO.NET connection for a connection string. Virtual so
    /// tests can substitute a connection whose <c>OpenAsync</c> fails.
    /// </summary>
    /// <param name="connectionString">The ADO.NET connection string.</param>
    /// <returns>A new <see cref="DbConnection"/> for the given connection string.</returns>
    internal virtual DbConnection CreateConnection(string connectionString) =>
        new SqlConnection(connectionString);

    /// <inheritdoc />
    public async Task CachedWriteAsync(
        string connectionName,
        string sql,
        IReadOnlyDictionary<string, object?>? parameters = null,
        string? originInstanceName = null,
        CancellationToken cancellationToken = default,
        TrackedOperationId? trackedOperationId = null,
        Guid? executionId = null,
        string? sourceScript = null,
        Guid? parentExecutionId = null)
    {
        var definition = await ResolveConnectionAsync(connectionName, cancellationToken);
        if (definition == null)
        {
            throw new InvalidOperationException($"Database connection '{connectionName}' not found");
        }

        if (_storeAndForward == null)
        {
            throw new InvalidOperationException("Store-and-forward service not available for cached writes");
        }

        var payload = JsonSerializer.Serialize(new
        {
            ConnectionName = connectionName,
            Sql = sql,
            Parameters = parameters
        });

        // ExternalSystemGateway-015: the entity's MaxRetries is a non-nullable int
        // whose default is 0, and the Store-and-Forward engine interprets a stored
        // MaxRetries of 0 as "no limit" (retry forever) — see
        // StoreAndForwardMessage.MaxRetries ("0 = no limit") and the retry-sweep
        // guard `MaxRetries > 0 && ...`. Passing 0 verbatim would turn every
        // unconfigured cached write into an unbounded retry loop. A 0 is treated as
        // "unset" and passed as null so the bounded S&F default applies; the
        // RetryDelay default of TimeSpan.Zero is likewise unset.
        await _storeAndForward.EnqueueAsync(
            StoreAndForwardCategory.CachedDbWrite,
            connectionName,
            payload,
            originInstanceName,
            definition.MaxRetries > 0 ? definition.MaxRetries : null,
            definition.RetryDelay > TimeSpan.Zero ? definition.RetryDelay : null,
            // Audit Log #23 (M3): pin the S&F message id to the
            // TrackedOperationId so the retry loop (Bundle E Tasks E4/E5) can
            // read it back via StoreAndForwardMessage.Id and emit per-attempt +
            // terminal cached-write telemetry. Null -> S&F mints its own GUID
            // (legacy pre-M3 behaviour).
            messageId: trackedOperationId?.ToString(),
            // Audit Log #23 (ExecutionId Task 4): thread the originating script
            // execution's ExecutionId + SourceScript onto the buffered row so
            // the retry-loop cached-write audit rows carry the same provenance
            // the script-side cached rows do.
            executionId: executionId,
            sourceScript: sourceScript,
            // Audit Log #23 (ParentExecutionId Task 6): thread the spawning
            // inbound-API request's ExecutionId onto the buffered row so the
            // retry-loop cached-write audit rows correlate back to the
            // cross-execution chain. Null for a non-routed run.
            parentExecutionId: parentExecutionId);
    }

    /// <summary>
    /// WP-9/10: Delivers a buffered CachedDbWrite during a store-and-forward retry
    /// sweep — executes the SQL against the named connection. Returns true on
    /// success, false if the connection no longer exists (the message is parked);
    /// throws on any execution error so the engine retries.
    /// </summary>
    /// <param name="message">The buffered store-and-forward message to deliver.</param>
    /// <param name="cancellationToken">Cancellation token for the delivery operation.</param>
    /// <returns>A task that resolves to <c>true</c> on success, or <c>false</c> if the connection no longer exists.</returns>
    public async Task<bool> DeliverBufferedAsync(
        StoreAndForwardMessage message, CancellationToken cancellationToken = default)
    {
        // ExternalSystemGateway-018: a malformed (not just empty/null-fielded)
        // PayloadJson would otherwise throw `JsonException` here, which the S&F
        // engine treats as a transient failure and retries forever (poison
        // message). Re-running the same deserialization against the same payload
        // will throw deterministically, so JsonException is permanent — log,
        // and return false so the S&F engine parks the message instead.
        CachedWritePayload? payload;
        try
        {
            payload = JsonSerializer.Deserialize<CachedWritePayload>(message.PayloadJson);
        }
        catch (JsonException ex)
        {
            _logger.LogError(
                ex,
                "Buffered CachedDbWrite message {Id} has malformed JSON payload; parking.",
                message.Id);
            return false;
        }

        if (payload == null || string.IsNullOrEmpty(payload.ConnectionName) || string.IsNullOrEmpty(payload.Sql))
        {
            _logger.LogError("Buffered CachedDbWrite message {Id} has an unreadable payload; parking.", message.Id);
            return false;
        }

        var definition = await ResolveConnectionAsync(payload.ConnectionName, cancellationToken);
        if (definition == null)
        {
            _logger.LogError(
                "Buffered DB write to '{Connection}' cannot be delivered — the connection no longer exists; parking.",
                payload.ConnectionName);
            return false;
        }

        await using var connection = new SqlConnection(definition.ConnectionString);
        await connection.OpenAsync(cancellationToken);
        using var command = connection.CreateCommand();
        command.CommandText = payload.Sql;
        if (payload.Parameters != null)
        {
            foreach (var (key, value) in payload.Parameters)
            {
                var parameter = command.CreateParameter();
                parameter.ParameterName = key.StartsWith('@') ? key : "@" + key;
                parameter.Value = JsonElementToParameterValue(value);
                command.Parameters.Add(parameter);
            }
        }
        await command.ExecuteNonQueryAsync(cancellationToken);
        return true;
    }

    // ExternalSystemGateway-020: a JSON number that does not fit in Int64 must
    // prefer decimal over double — a script's decimal SQL parameter is
    // serialised as JSON without a type tag, and downcasting it to double on
    // the cached-write retry path silently loses precision (e.g.
    // 1234567890.1234567890 -> 1234567890.1234567 as a binary float). Probe
    // long first (whole-number fast path), then decimal (preserves authored
    // precision for typical money/measurement values), and only fall through
    // to double for genuinely out-of-decimal-range values (very large
    // scientific-notation floats).
    /// <summary>
    /// Converts a <see cref="JsonElement"/> to the most appropriate SQL parameter value,
    /// preferring <c>long</c> → <c>decimal</c> → <c>double</c> for numeric kinds to preserve precision.
    /// </summary>
    /// <param name="element">The JSON element to convert.</param>
    /// <returns>A boxed CLR value suitable for use as an ADO.NET parameter, or <see cref="DBNull.Value"/> for null/undefined.</returns>
    internal static object JsonElementToParameterValue(JsonElement element) => element.ValueKind switch
    {
        JsonValueKind.String => (object?)element.GetString() ?? DBNull.Value,
        JsonValueKind.Number => element.TryGetInt64(out var l)
            ? l
            : element.TryGetDecimal(out var dec)
                ? dec
                : element.GetDouble(),
        JsonValueKind.True => true,
        JsonValueKind.False => false,
        JsonValueKind.Null or JsonValueKind.Undefined => DBNull.Value,
        _ => element.GetRawText()
    };

    private sealed record CachedWritePayload(
        string ConnectionName,
        string Sql,
        Dictionary<string, JsonElement>? Parameters);

    private async Task<DatabaseConnectionDefinition?> ResolveConnectionAsync(
        string connectionName,
        CancellationToken cancellationToken)
    {
        // ExternalSystemGateway-011: name-keyed repository lookup instead of
        // fetch-all-then-filter — connection definitions are resolved on every
        // cached write / connection request, so the repository performs an indexed
        // query rather than loading every connection into memory.
        return await _repository.GetDatabaseConnectionByNameAsync(connectionName, cancellationToken);
    }
}